Local exhaust ventilator with rotating swirler

ABSTRACT

The present invention relates to a local exhaust ventilator which has a rotating swirler to make a swirl flow for increasing exhaust efficiency by expanding an exhaust region. Disclosed is a local exhaust ventilator with a simplified structure, wherein noise due to interference of turbulence is reduced and exhaust gas is removed at a wide area. The local exhaust ventilator includes a disk-shaped swirler rotatably mounted at an exhaust tube, a wing installed at the swirler perpendicular thereto to form a swirl flow, and a driving unit installed at the exhaust tube to rotate the swirler.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to an exhaust ventilator, and, inparticular, to a local exhaust ventilator which has a rotating swirlerto produce a swirl flow for increasing exhaust efficiency by expandingan exhaust region.

(b) Description of the Related Art

Generally local exhaust ventilators are utilized in homes, restaurants,and factories that generate pollutants, and, in particular, they can beused where local pollutants are produced far from a main ventilator,where the ventilator is not easily installed near the source of thepollutants, and where the pollutants are produced momentarily.

However, conventional local exhaust ventilators for these purposes havesome shortcomings, as follows. The capture speed necessary for theremoval of the pollutants decreases rapidly along the axial direction sothat the conventional local exhaust ventilators are not effective toeliminate pollutants occurring far from the exhaust pipe, and,therefore, the exhaust pipe needs to be installed as near to the sourceof the pollutants as possible. The near-installed exhaust pipe, however,can be an obstacle to a working line, and is inefficient for pollutantremoval due to workers moving around near the exhaust pipe.

In order to overcome these shortcomings of the conventional localexhaust ventilators, swirl flow has been introduced to an exhaustventilator, which blows a similar amount of air to that of the exhaustedair into the surrounding space. The blown air produces a swirl flow thatincreases the exhaust efficiency by using the concentrated swirl flow inthe intake process of the exhaust ventilator.

Such an exhaust ventilator, however, makes noises resulting from theturbulence generated by the interference between the flow being drawnand the flow being blown in the narrow area under the exhaust pipe, andraises the possibility of spreading the pollutants farther in the spaceby the blown flow. Also, additional facilities, such as a flow pipe, afilter, and a blower, are required to generate the swirl flow.

SUMMARY OF THE INVENTION

In accordance with the present invention, a local exhaust ventilator isprovided that reduces noise due to turbulence-induced interference andremoves exhaust gas over a larger area.

Further in accordance with the present invention, a local exhaustventilator is provided that involves a simplified structure, an economicproduction cost, and easy installation, maintenance, and repair.

The present invention discloses a local exhaust ventilator comprising adisk-shaped swirler rotatably mounted at an exhaust tube, a winginstalled at the swirler perpendicular thereto to form a swirl flow, anda driving unit installed at the exhaust tube to rotate the swirler.

The wing may have a linear structure or a curved structure bent towardthe central axis of the swirler.

The angle between the rotation axis of the swirler and an inclined sideof the swirler may be in the range from 60° to 120°. The wing may bespaced apart from the exhaust tube a predetermined distance, and beelongated outwardly such that the length of the wing is enlarged.

The driving unit may have a structure where the swirler is rotatablyfitted to the outer circumference of the exhaust tube via a bearing witha circular rack mounted along the top thereof, and a pinion gear may beinstalled at the rotation shaft of a driving motor provided external tothe exhaust tube while being coupled to the rack.

In accordance with one form of the present invention, a local exhaustventilator is provided that increases exhaust efficiency by radial swirlflow entraining air from above an exhaust pipe. A swirler, which is anannular plate with blades, is installed in an exhaust pipe and rotatesinside a swirler cover having a peripheral gap along the outer surfaceof the exhaust pipe and another peripheral gap along the outer rim ofthe swirler cover.

Further in accordance with one form of the present invention, a localexhaust ventilator is provided in which a protective cover for therotating swirler secures the safety of workers moving around under thesystem. In another exemplary embodiment of the present invention, alocal exhaust ventilator includes a swirler, a swirler cover, and adriving unit.

The swirler may include an annular plate positioned near an inlet of anexhaust pipe and which rotates about the axis of the exhaust pipe, and aplurality of blades which are placed along an outer rim of the annularplate, each blade being fixed in the radial direction on the annularplate while protruding toward the exhaust pipe.

The swirler cover may include a ring-shaped top cover which covers a topof the blades and provides a first gap between an outer surface of theexhaust pipe and inner rim of the top cover, and a ring-shaped bottomcover which covers a bottom of the blades and is positioned apart fromthe top cover by a second gap.

The driving unit may be installed within the exhaust pipe and rotatesthe swirler by way of a swirler shaft attached thereto.

The gap space between the top cover and the bottom cover of the swirlercover may decrease in height as the distance from the rotational axis ofthe swirler increases in a radial direction.

Also, with a swirler cover, the top cover has a hole larger than theouter diameter of the exhaust pipe, and the bottom cover has a hole witha diameter close to the inner diameter of the exhaust pipe.

Each blade may be formed in a streamlined shape with the height of eachswirler blade decreasing as the distance from the rotational axis of theswirler increases in a radial direction, and the top cover of theswirler cover may be formed in a shape contoured to the shape of theswirler blade.

The outer portion of the swirler blade can extend in a radial directionbeyond the outer rim of the annular plate. Each swirler blade may bestraight in a radial direction or curved toward the perimeter of theannular plate. Each blade of the swirler can be fixed perpendicular tothe surface of the annular plate.

The driving unit may include a driving motor mounted inside the exhaustpipe by brackets, and a driving rod of the driving motor fixed at thecenter of rotation of the swirler and which rotates the swirler.

According to one form of the local exhaust ventilator of the presentinvention, the swirler is operated with the instant generation of alocal contamination source, thereby enhancing the energy efficiency.Furthermore, a tornado-like flow is induced due to the interactionthereof with the ground surface, thereby removing the contaminationsource generated at the ground in an effective manner.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other advantages of the present invention will become moreapparent by describing embodiments thereof in detail with reference tothe accompanying drawings, in which:

FIG. 1 is a schematic longitudinal sectional view of a local exhaustventilation system according to an embodiment of the present invention;

FIG. 2 is a schematic longitudinal sectional view of a local exhaustventilation system according to another embodiment of the presentinvention;

FIG. 3 illustrates a swirler installed at the local exhaust ventilatoraccording to an embodiment of the present invention;

FIG. 4 illustrates a variant of the swirler shown in FIG. 3;

FIG. 5 is a perspective external view of a swirler with a protectionunit;

FIGS. 6A and 6B illustrate the operational state of the local exhaustventilator according to an embodiment of the present invention,depending upon the rotation speed of the swirler;

FIGS. 7A and 7B illustrate the operational state of the local exhaustventilator according to an embodiment of the present invention,depending upon the angle of the swirler;

FIG. 8 is a longitudinal sectional view of a local exhaust ventilatoraccording to an exemplary embodiment of the present invention;

FIG. 9 is a transverse sectional view of a local exhaust ventilatoraccording to an exemplary embodiment of the present invention; and

FIG. 10 is a transverse sectional view of a local exhaust ventilatoraccording to another exemplary embodiment of the present invention.

DETAILED DESCRIPTION

The present invention will be described more fully hereinafter withreference to the accompanying drawings, in which various embodiments ofthe invention are shown.

As shown in FIG. 1, the local exhaust ventilator includes a swirler 10installed at an exhaust tube 50 to form a swirl flow, and a driving unitfor rotating the swirler 10.

Swirlers are largely classified into an inner drive type and an outerdrive type. With the inner drive type shown in FIG. 1, the driving unitis formed with a driving motor 20 fixed to the inner circumference ofthe exhaust tube 50 via a bracket 21. The swirler 10 rotates around therotation shaft of the driving motor 20 extended external to the exhausttube 50 while being fixed thereto.

Furthermore, with the outer drive type shown in FIG. 2, the swirler 10is installed at the outer circumference of the exhaust tube 50 via abearing 30 such that it can be rotated. A circular rack 31 is mounted onthe top of the swirler 10. A driving motor 32 is installed external tothe exhaust tube 50, and a pinion gear 33 is provided at the rotationshaft of the driving motor 32 and coupled to the rack 31.

With the above structure, the driving power of the driving motor 32 istransmitted to the swirler 10 via the rack 31 and the pinion gear 33 tothereby rotate the swirler 10.

The outer drive type is more preferable than the inner drive type inthat the swirler, the bearing, and the motor can be modulated in asimplified manner while being attached to the common exhaust tube 50,and motor failure due to the contamination source can be minimized.

The driving unit is not limited to the above structure, but may bear anyother structure provided that the swirler 10 can rotate around thecentral axis of the exhaust tube 50.

The swirler 10 rotates around the exhaust tube 50 to generate a swirlflow. The swirler 10 is formed with a disk body and a wing 11 verticallyinstalled at the bottom of the disk body.

The wing 11 substantially generates the swirl flow when the swirler 10is rotated. The swirl flow characteristic is varied depending upon theinstallation direction or location of the wing 11 with respect to theswirler 10. The wing 10 may be installed distant from the central axisof the swirler 10, or close thereto with a linear or curved structure.

FIG. 3 illustrates the curved structure of the wing 11 bent toward thecentral axis of the swirler 10, and FIG. 4 illustrates the linearstructure thereof.

Furthermore, the driving speed (the rotation speed) of the swirler 10influences the air flow around the exhaust tube 50. It is preferable torotate the swirler 10 at 1300˜1700 rpm.

A protection cover may be installed external to the swirler to protectthe facility, and prevent possible safety failures due to the high speedrotation of the swirler.

As shown in FIG. 5, the cover has a disk-shaped top cover 60 installedat the exhaust tube 50 while being extended to the backside of theswirler 10, a donut-shaped bottom cover 61 placed forward of the wing 11of the swirler 10, and supports 62 vertically installed at the frontalend of the top cover 60 while being spaced apart from each other by apredetermined distance to support the bottom cover 61.

The swirler 10 and the wing 11 are protected by the top cover 60 and thebottom cover 61, and the lateral side of the wing 11 disposed betweenthe bottom cover and the top cover opens to blow the air for forming theswirl flow.

The operation principle of the local exhaust ventilator according to thepresent invention will be now explained.

When the swirler 10 is rotated with the exhaust operation shown in FIG.6A, the air flow made below the swirler 10 is simultaneously influencedby the centrifugal force and the centripetal force due to the exhaustoperation so that it is not moved in the radial direction, but isrotated by the rotation speed of the swirler 10. In this case, the flownot moved in the radial direction is like an imaginary flux wall (aircurtain).

The local exhaust ventilator is operated while constantly maintainingthe amount of exhaust gas so that it takes in the air below the aircurtain rather than the air external to the air curtain. The airexpelled to the outside by the swirler 10 is introduced to the locationof the intake air, and is directed toward the exhaust tube 50. Based onsuch an operation principle, as shown in FIG. 6A, a secondary swirl flow40 is formed below the swirler 10 while being rotated in the directionperpendicular to the rotation direction of the swirler 10. Of course,the secondary swirl flow is a part of the primary swirl flow (aircurtain) rotated around the axis of the exhaust tube 50.

The secondary swirl flow 40 continually receives the required energy bythe swirler 10, and rotates at a predetermined speed so that it has arole of intruding the air below the secondary swirl flow 40 into theexhaust tube 50. In this way, the influential area of the exhaust flowis amplified downwards while enlarging the ventilating area.

The formation location of the secondary swirl flow 40 is varieddepending upon the rotation speed of the swirler 10. As shown in FIG.6B, when the rotation speed of the swirler increases, the effect of thecentrifugal force increases so that the secondary swirl flow 40 isgenerated at the area more distant from the swirler.

With the lower rotation speed of the swirler 10, the secondary swirlflow 40 is formed below the swirler so that a complicated and strongturbulence is formed below the swirler with increased noise.Furthermore, as the contaminants are diffused within the turbulence, thecontamination source in the exhaust flow is liable to be diffused. Bycontrast, when the secondary swirl flow 40 is formed distant from theswirler, the noise is diminished due to the clear isolation of thesecondary swirl flow 40 from the exhaust flow, and the diffusionpossibility of the contamination source due to the swirler is removed.Furthermore, a wide ventilating area is formed due to the secondaryswirl flow 40 spread external to the swirler.

The flow characteristic is influenced by the shape of the swirler, thatis, the size and axial angle thereof. As the radius of the swirler isincreased, the swirl flow becomes stronger, and the exhaust depthbecomes enlarged at the same rotation speed. As shown in FIG. 6A, theswirler 10 commonly proceeds perpendicular to the axis thereof.

As shown in FIG. 7A, when the angle θ between the rotation axis and theinclined side of the swirler 10 is in the range from 60° to 90°, thesecondary swirl flow 40 can be brought downwards close to the ground. Asshown in FIG. 7B, the angle θ between the rotation axis and the inclinedside of the swirler 10 is in the range from 90° to 120°, the exhaustdepth is decreased compared to the case where the inclined side isangled at 90°, but the secondary swirl flow 40 is stabilized so that thenoise is reduced and the exhaust flow is also formed in a stable manner.

It is also preferable to shape the wing 11 attached to the swirler 10correctly. With the rotation of the swirler 10, the flow around theswirler is rotated due to the Wing 11 attached to the swirler.Therefore, with a larger sectional area of the wing, the amount of flowto be rotated is increased. As the rotation speed of the swirler ishigher with the larger radius, the outer length of the wing should beelongated. Furthermore, in order to prevent the contamination sourcefrom being diffused due to the swirler, the wing should be attached tothe swirler while being spaced apart from the exhaust tube 50 by apredetermined distance. In order to extrude a larger amount of flow tothe outside, it may be considered to make a linear wing as well as acurved wing.

FIG. 8 is a longitudinal sectional view of a local exhaust ventilatoraccording to an exemplary embodiment of the present invention, and FIG.9 is a transverse sectional view of a local exhaust ventilator accordingto an exemplary embodiment of the present invention.

According to the embodiment, a local exhaust ventilator 60 includes aswirler 70 which is installed in the vicinity of an inlet of the exhaustpipe 62 and produces a swirl flow while rotating, a swirler cover 80which covers the top and the bottom of the blades 77 of the swirler 70,and a driving unit 90 which is mounted within the exhaust pipe 62 androtates the swirler 70.

The swirler 70 includes an annular plate 73 which is placed near the endof the exhaust pipe 62 and rotates about the axis of the exhaust pipe62, and a plurality of blades 77 which are placed along the outer rim ofthe annular plate 73 and are attached vertically in a radial directionon the annular plate 73. Each blade 77 protrudes toward the exhaust pipe62.

The annular plate 73 has a hole of at least the same size as the innerdiameter of the exhaust pipe 62, and the outer diameter of the annularplate 73 is larger than that of the exhaust pipe 62. The annular plate73 has a plurality of spokes 75 connecting the center of rotation 71 ofthe swirler 70 to the inner rim of the annular plate 73. Because thespokes 75 are positioned at the inlet of the exhaust pipe 62, aboutthree spokes, as seen in FIG. 8 and FIG. 9, are preferable, in order notto block the incoming flow through the inlet of the exhaust pipe 62.

The blades 77 placed around the outer rim of the annular plate 73 arepreferably fixed vertically on the top surface of the annular plate 73,with the outer portion of the blades extending in the radial directionbeyond the outer rim of the annular plate 73. Each blade 77, as seen inFIG. 8, has a streamlined shape of which the height decreases with anincrease in the distance from the rotational axis. Because the blade 77serves as a working part of the swirler 70 for producing the swirl flow,the blade 77 with the streamlined shape can draw a large quantity of airfrom above the inlet of the exhaust pipe 62 and then exhaust it in aradially outward direction.

Also, each blade 77 is straight in the radial direction as seen in FIG.9.

The swirler cover 80 includes a top cover 82 covering the top of theblade 77, and a bottom cover 86 covering the bottom of the blade 77.

The top cover 82 is in a ring shape which has a hole larger than theouter diameter of the exhaust pipe 62, and is positioned to form a firstgap I between the outer surface of the exhaust pipe 62 and the inner rimof the top cover 82. And, the bottom cover 86 is in a ring shape whichhas a hole with a diameter similar to the inner diameter of the exhaustpipe 62, and is positioned apart from the top cover 82 to form a secondgap II between the outer rims of both the bottom cover 86 and the topcover 82.

In particular, the top cover 82 is in a rounded shape contoured to theshape of the blades 77 such that the height of the top cover 82increases as the distance from a center of rotation 71 of the swirler 70decreases, and the height of the top cover 82 decreases as the distancefrom the center of rotation 71 of the swirler 70 increases. The bottomcover 86 is formed in a flat shape, and therefore the gap space betweenthe top cover 82 and the bottom cover 86 decreases as the distance fromthe rotational axis of the swirler decreases in the radial direction.Due to this particular shape, the swirler cover 80 makes the air drawnby the swirler 70 accelerate through the radially contracted space andproduces the strong swirl flow when the air is expelled to the outside.

The swirler cover 80 also protects the blade 77 by covering both the topand bottom of the blade 77.

The top cover 82 is mounted on the outside of the exhaust pipe 62 by aplurality of supporting rods 58. In order to not block the air flowthrough the first gap I between the outer surface of the exhaust pipe 62and the top cover 82, the supporting rods 58 are preferably positionedequidistant to each other, and four or six supporting rods may be used.

A plurality of guide blades 84 connect the top cover 82 to the bottomcover 86 at the outer portions of both the top cover 82 and bottom cover86. The guide blade 84 positioned in the radial direction along theperimeter is attached vertically to both the top cover 82 and the bottomcover 86. It is preferable for the guide blades 84 to be uniformlyplaced equidistantly. Each of the guide blades 84 may be placed at aposition corresponding to each blade 77, and the number of guide blades84 may be the same as the number of the blades 77. However, there is norestriction in the number and the position of the guide blades 84 withrespect to the blades 77. Therefore, each of the guide blades 84 seen inFIG. 9 is straight in the radial direction in the illustratedembodiment.

The swirler 70 is rotated by a driving unit, as illustrated in FIG. 8,including a driving motor 93 which is mounted inside the exhaust pipe 62by brackets 91, and a driving rod 95 of the driving motor 93 thatextends to the end of the exhaust pipe 62 and is fixed at the center ofrotation 71 of the swirler 70. However, the driving unit 90 of thepresent invention does not necessarily have this configuration only, andit can have any configuration such that it can rotate the swirler aboutthe axis of the exhaust pipe.

On the other hand, the swirler 70, the swirler cover 80 and the drivingunit 90, as described above, can be assembled in a single module whichcan be attached to an existing exhaust pipe directly and usedimmediately.

As seen in FIG. 10, the local exhaust ventilator of the illustratedembodiment is the same as that of the previous embodiment except for theshapes of the blades 102 attached vertically to the annular plate 73 andof the guide blades 104 connecting the top cover 82 to the bottom cover86 around the outer rims thereof and forming a gap between them.

The blades 102 of the swirler in the illustrated embodiment are curvedtoward the perimeter of the annular plate 73, and the guide blades 104are also curved toward the perimeter of the bottom cover 86. It ispreferable that the curvature of the blades 102 is opposite to that ofthe guide blades 104. The opposite curvature plays a role in helping theair accelerated by the swirler 70 to have a strong swirl flow.

Following is the working principle of the local exhaust ventilator ofthe present invention.

Under the proper working state, as illustrated in FIG. 8, the flow aabove the inlet of the exhaust pipe 62 is pulled by the rotating swirler70 through the first gap I to the inside of the swirler cover 80, and ispushed radially by the swirler blade 77 to the outside through thesecond gap II while forming the swirl flow b. At this time, the air isaccelerated and expelled by the swirler cover 80 and the guide blade 84while maintaining the swirl component. The flow below the inlet of theexhaust pipe 62 is divided into two kinds of flow by the acceleratedoutgoing swirl flow: one flow c is pushed radially outward; and theother flow d is entrained by the exhaust ventilator 60 toward the axisof the exhaust pipe 62. Because the flow rate of the exhaust ventilator60 is kept constant under the working state, the exhaust ventilator 60exhausts an additional volume of air which is the same amount as the airpushed in the radial direction. Therefore, the interaction between thesetwo kinds of flow expands the exhaust region in the axial direction.

The radially pushed swirl flow c and d moves toward the axis of theexhaust pipe 62 because of the exhausting process, and forms thesecondary swirl flow e under the swirler 70. The secondary flow e keepsrotating at a constant speed with the energy supplied by the swirler 70,and plays a role in pushing the air under the secondary swirl flow intothe exhaust pipe 62. By this principle, the air is accelerated towardthe inlet of the exhaust pipe 62 so that the exhaust region expands.

Also, as the swirl flow that is widely spread in the radial direction isentrained toward the axis of the exhaust pipe 62 by the exhaustingprocess, the rotation of the swirl flow becomes more vigorous by theconservation of the angular momentum. This causes a low pressuredistribution under the exhaust pipe 62 which strongly boosts the exhaustflow.

As explained above, the local exhaust ventilator using the swirler ofthe present invention can enhance the performance of exhaust ventilationby making a radial swirl flow which is produced by a swirler, a swirlercover, and air entrained from above the inlet of an exhaust pipe. Also,it can prevent pollutants from being rebroadcast and can make itpossible for the efficient removal of the pollutant occurring in a localarea.

Since the swirler, the swirler cover, and the driving unit can beassembled in a single module which can be simply attached to an existingexhaust pipe, there is no need for further investment in the facility.

In addition, the safety of workers near the local exhaust ventilator canbe secured by the swirler cover which surrounds the swirler blades thatrotate at a high speed.

Although various embodiments of the present invention have beendescribed in detail hereinabove, it should be dearly understood thatmany variations and/or modifications of the basic inventive conceptsherein taught which may appear to those skilled in the art will stillfall within the spirit and scope of the present invention, as defined inthe appended claims.

1. A local exhaust ventilator comprising: a disk-shaped swirlerrotatably mounted at an exhaust tube; a wing installed at the swirlerperpendicular thereto to form a swirl flow; and a driving unit installedat the exhaust tube to rotate the swirler.
 2. The local exhaustventilator of claim 1, wherein the wing has a linear structure.
 3. Thelocal exhaust ventilator of claim 1, wherein the wing has a curvedstructure bent toward the central axis of the swirler.
 4. The localexhaust ventilator of claim 1, wherein the angle between the rotationaxis of the swirler and an inclined side of the swirler is in the rangefrom 60° to 120°.
 5. The local exhaust ventilator of claim 4, whereinthe wing is spaced apart from the exhaust tube by a predetermineddistance, and is elongated outwardly such that the length of the wing isenlarged.
 6. The local exhaust ventilator of claim 1, wherein thedriving unit has a structure where the swirler is rotatably fitted tothe outer circumference of the exhaust tube via a bearing with acircular rack mounted along the top thereof, and a pinion gear isinstalled at the rotation shaft of a driving motor provided external tothe exhaust tube while being coupled to the rack.
 7. A local exhaustventilator comprising: a swirler comprising an annular plate which isplaced near an inlet of an exhaust pipe and which rotates about an axisof the exhaust pipe, and a plurality of blades which are placed along anouter rim of the annular plate, each blade being fixed in the radialdirection on the annular plate while protruding toward the exhaust pipe;a driving unit installed within the exhaust pipe and having a shaft ofthe swirler attached thereto for rotating the swirler.
 8. The localexhaust ventilator of claim 7, further comprising a swirler covercomprising a ring-shaped top cover which covers a top of the blades andprovides a first gap between an outer surface of the exhaust pipe and aninner rim of the top cover, and a ring-shaped bottom cover which coversa bottom of the blades and is positioned apart from the top cover by asecond gap.
 9. The local exhaust ventilator of claim 8, wherein theswirler cover forms a gap space between the top cover and the bottomcover such that the gap space decreases in height as the distance fromthe rotational axis of the swirler increases in a radial direction. 10.The local exhaust ventilator of claim 8, wherein the top cover has ahole with a diameter larger than the outer diameter of the exhaust pipe,and the bottom cover has a hole with a diameter close to the innerdiameter of the exhaust pipe.
 11. The local exhaust ventilator of claim8, wherein each blade is in a streamlined shape of which the heightdecreases as a distance from the rotational axis of the swirler isincreased in a radial direction.
 12. The local exhaust ventilator ofclaim 11, wherein the top cover of the swirler cover is formed in ashape contoured to the shape of the blade of the swirler.
 13. The localexhaust ventilator of claim 8, wherein the outer portion of the bladeextends in a radial direction beyond the outer rim of the annular plate.14. The local exhaust ventilator of claim 8, wherein each blade of theswirler is straight in a radial direction.
 15. The local exhaustventilator of claim 8, wherein each blade of the swirler is curvedtoward the perimeter of the annular plate.
 16. The local exhaustventilator of claim 8, wherein each blade of the swirler is fixedperpendicular to the surface of the annular plate.
 17. The local exhaustventilator of claim 8, wherein the driving unit comprises a drivingmotor which is mounted inside the exhaust pipe by brackets, and adriving rod of the driving motor which is fixed at the center ofrotation of the swirler and which rotates the swirler.